Electric valve converting system



Sept. 7, 1937. B. D. BEDFORD 20,493

ELECTRIC VALVE CONVERTING SYSTEM Original Filed Aug. 25, 1953 Inventor:Bur-n6 ce D. Be dford,

by a 3 His Attorney.

Reicsued Sept. 7, 1937 UNITED STATES PATENT OFFICE ELECTRIC VALVECONVERTING SYSTEM Burnice D. Bedford, Schenectady, N. Y., aasignor .toGeneral Electric Commy, a corporation of 1 New York 37 Claims. (01.172-281) My invention relates to electric valve converting system fortransmitting energy between independent alternating current circuits ofdifferent frequencies and more particularly to improved excitationapparatus for such converting systems which will enable the systems tooperate satisfactorily under widely variable load condi provide a newand improved electric valve contlons.

In United States Letters Patent No. 1,930,303, granted April 15, 1933,upon my application, there are disclosed several electric valvefrequency changing systems for transmitting energy between alternatingcurrent circuits of different frequencies, together with excitationapparatus therefor, suitable for transmitting energy to a; leading orlagging power factor alternating current load circuit. My presentinvention constitutes an improvement upon that which forms the subjectmatter of the above mentioned patent and is directed principally toimproving the load conditions, this angle being known as the commutatingangle. Under light load conditions it is desirable to have thiscommutating angle a minimum in order to prevent unnecessary distortionof the wave-form of theoutput voltage.

Many of such converting systems also have substantial natural voltageregulation so that it isdesirable to compensate or compound for thisnatural regulation by advancing the phase of the component of rectifierexcitation. Again when it is desired to transmit energy between twocircuits having a non-integral frequency ratio, the output voltage wavegenerally comprises a series of input half cycles and intermittently thenumber of half cycles isincreased by one to take careof the frictionalrelationship in the frequencies of the circuits. If these additionalinput half cycles are added to even numbered half cycles of the loadfrequency, certain portions of the converting system will carry aresultant unidirectional component of current which will tend tosaturateany' transformer windings included in this circuit. 'Myinvention comprises an improved electric valve converting system and animproved excitation apparatus therefor which. will provide a solution tothe above mentioned problems and which will considerably simplify theexcitation apparatus of the converting systems of the prior art.

It is an object of my invention, therefore, to

verting system and an improved grid excitation apparatus therefor whichwill simplify the systerns of the prior art and which will solve theabove mentioned problems.

It is another object of my invention to'provide a new and improved valveconverting system and an excitation apparatus therefor which willautomatically regulate the output voltage ofthe system to compensate forits natural regulation characteristics.

It is a further object of my invention to provide an improved electricvalve converting system, and an excitation apparatus therefor, suitablefor transmitting energy from an alternating current supply circuit to analternating current load circuitfunder reactive power conditions bymeans of which the commutating angle of the electric valves operating asinverters will be varied in accordancewith the load transmitted by theapparatus.

It is a still further object of my invention to provide an improvedelectric valve converting system and an excitation apparatus thereforsuitable for transmittingv energy between alternating current circuitsvhaving anon-integral frequency ratio by means of which the currenttransmitted by the several groups of electric valves will beautomatically balanced.

In accordance with my invention, alternating current circuits ofdifferent frequencies are interconnected through a plurality of groupsof electrio-valves. The circuits of diiferent frequencies will bereferred to hereinafter as the higher frequency circuit and the lowerfrequencycircuit, re-

spectively, but it is to be understood that the terms higher and lowerare used only in a relative sense and that my invention is not limitedto any particular order of magnitude for the frequencies of therespective circuits. The several electric valves are excited forinverter operation'to transmit energy from the lower frequency circuitto the higher frequency circuit and there is provided means formodifying the inverter excitation to increase the commutating angle ofthe inverting valves with an increase in load current of the system.There is also provided a component of rectifier excitation for theseveral groups of valves and this rectifier excitation is periodicallyand successively removed from the several groups of valves at thefrequency of the lower frequency circuit so that the groups.

of valves act successively as the rectifiers supplying successive halfcycles of alternating current to the load circuit.

In order to prevent a simultaneous flow of current of more than apredetermined magnitude in more than one group of electric valves, whichwould tend to become a short circuit on one or both of the supply andload circuits, there is provided a means responsive to the flowoi'current in each group of valves for removing the rectifier excitationfrom the other valves. This rectifier excitation is also varied inresponse to the load current transmitted by the system to compensate forthe natural regulation characteristics of the system. To provide for thecase in which the system is to transmit energy between alternatingcurrent circuits having a non-integral frequency ratio, there isprovided means responsive to an unbalance in the current transmitted bythe several groups of valves to modify the rectifier excitation of thesegroups of valves in such a way as to restore this balance and thusprevent any unidirectional component in the transformer windings of thesystem which would tend to saturate them.

For a better understanding of my invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing in which the singlefigure diagrammatically illustrates my invention as applied to a systemfor transmitting energy from a three-phase alternating current supplycircuit of higher frequency to a single phase alternating current loadcircuit of lower frequency.

Referring more particularly to the drawing, there is shown a system fortransmitting energy from a three-phase higher frequency alternatingcurrent supply circuit III to a single phase lower frequency alternatingcurrent load circuit .I I.

This apparatus includes a transformer bank provided with a three-phaseprimary network 4 2 connected to the supply circuit III and a pair ofsix-phase star connected secondary networks I3 and I4 connected tosupply opposite halves of the primary winding of an output transformerI5, the secondary winding of which is connected to the circuit II. Thenetworks I3 and supply their respective portions of the primary windingof the transformer I5 through a plurality of electric valves or electricvalve paths. These valves may be of any of the several types well knownin the art and may comprise a plurality of single anode, single cathodevalves or, as illustrated in the drawing,theymaycomprise amultiple-anode, single cathode vapor electric discharge device I6. Asillustrated in the drawing, the several phase terminals of the networkI3 are connected to the anodes I! of the discharge device It while theelectrical neutral of the network I3 is connected to one terminal of theprimary winding ofthe transformer I5. Similarly, the phase terminals ofthe network I4 are connected to the anodes I8 of the discharge device I6while its electrical neutral is connected to the other terminal of theprimary winding of the transformer I5, the electrical neutral of thislatter winding being connected to the cathode of the electricaldischarge device I6 through a current smoothing reactance device 2|. Thegroups of anodes I1 and I8 are provided with associated control grids I9and 20,

respectively, connected to the cathode of the discharge device I4through current limiting resistors 22, appropriate windings of gridtransformers, which will be described in more detail hereinafter, and anegative bias battery 23.

In order to control the valve converting system to produce the objectsnoted above, there are provided a plurality of control transformers24-29, inclusive, to, provide rectifier excitation for the groups ofelectric valves or valve paths I1 and I8, and a group of controltransformers 30-35, inclusive, to provide inverter excitation for thesevalve paths. Each of the control transformers 24-29, inc1usive, isprovided with five groups of windings; the A windings, which are thesecondary, or output, windings for exciting the grids I9 and 20; the Bwindings, which are connected in series with the load current of theparticular group of valves which the transformers control; the Cwindings, which are connected in series with the load current of theother group of valves; the D windings, which are energized with a lowerfrequency alternating potential to periodically and successively removethe rectifier excitation, as will be described more fully hereinafter;and the E windings,'which are the main primary windings of the controltransformers and are energized from the alternating current supplycircuit In through any suitable phase shifting arrangement such, forexample, as ,a rotary phase shifting transformer 36.

Similarly the inverter excitation transformers 30-35, inclusive, areprovided with secondary or output windings F connected to the propercontrol grids I9 and 20; the windings G, connected in series with thecurrent transmitted by the valves which the transformers control; andthe windings H, which are the primary or excitation windings energizedfrom the alternating current supply circuit I0 through a suitable phaseadjusting means, such as a rotary phase shifting transformer 31.

It will be noted that the windings A and F are connected in series andthat each pair of windings AF is connected to the grid associated withthe anode which is connected to the particular phase terminal of thenetworks I3 or I4 corresponding to the phase from which the windings Eand H of the control transformers are energized. Thus,each grid receivestwo components of higher frequency alternating potential,one,a componentfor rectifier excitation approximately in phase, and the other, acomponent for inverter excitation approximately in phase opposition, tothe potential impressed upon its corresponding anode.

Unilaterally conductive devices, such as contact rectifiers 38, arepreferably connected in parallel to each of the windings A and F tobypass the negative half cycles of control potentials from the grids.Each of the control transformers 24-35, inclusive, is preferably of theself-saturating type so that it will become saturated from theenergization of the exciting windings E and H. The result is thatalternating potentials of a peaked wave form are impressed upon thegrids of the several valve paths. The control transformers 24-35,inclusive, are also designed to become saturated by predeterminedcurrents in other of their exciting windings, as will be explained inmore detail hereinafter.

As explained above, the windings D on the control transformers 24-29,inclusive, are for the purpose of periodically and successively removingthe rectifier excitation from the groups of control transformers 24, 25and 26, and 21, 28 and 29.

To this endthey may-be energizedfrom an auxiliary electric valverectifying circuit. In the particular converting circuit illustrated,the maximum duration of rectifier excitation, corresponding to unitypower factor on the load circuit II, is somewhat less than 180electrical degrees, referred to the load circuit. Under other powerfactor conditions, the periods of rectifier excitation are shorter, sothat the intervals during which rectifier excitation must be renewed aregreater than 180 electrical degrees. This result may be obtained byenergizing the windings D of the groups of transformers 24, 25, and 26and 21, 28, and 29 from the auxiliary electric valve rectifying circuits39 and 48, respectively. The

rectifier 39 comprises two phases of a supply transformer network 4| anda pair of electric valves 42 and 42, while the rectifier 48 comprisestwo phases of the network 4| and electric valves 44 and 45. The network4| may constitute the secondary network of a transformer having aprimary network 4| connected to a source of alternating current 41 of afrequency which it is desired to supply the load circuit although itwillbe understood that,if the circuit II is connected to an independentsource of electromotive force for determining its frequency, the network4| may be energized directly therefrom or the generator 41 may be drivenfrom a synchronous motor energized from the network Electric valves 42and 44 may be simple rectifier valves or their grids may be connected totheir anodes through current limiting resistors 46, as illustrated, toobtain an equivalent effect. The

grids of electric valves 42 and 45, however, are connected to theirrespective cathodes through current limiting resistors 46, negative biasbatieries 48 and secondary windings 49 and 50 of a transformer device5|, the primary winding 52 of which is energized from diametricallyopposite terminals of the network 4| through any suitable phaseadjusting means such as an impedance phue shifting circuit 52. Acapacitor 54 may be connected across the phase shifting circuit 53 tocompensate for the reactance of the transformer device 5| and contactrectifiers 55 may be connected across the windings 49 and 50, ifdesired, to shunt the negative half cycles of control potentials fromthe grids of electric valves 42 and 45. It will be noted that thewindings 49 and 50 are mounted on branches of the magnetic core of thedevice 5| having contracted or saturable sections, the result of whichis to convert the potential impressed upon the primary winding 52 intoalternating potentials of peaked wave form, a device well known in theart. The magnetic circuits of the windings 49 and 50 have a. commonmagnetic path or core sections 56 upon which are mounted windings 51 and58 connected in series with the 700 groups of anodes l1 and I8respectively. The

magnetic core section 56 is also provided with an additional winding 58which is short circuited through a low impedance device or resistor 60to short circuit any alternating component of a flux M produced in thecore section 56 by the windings 51 and 58. The magnetic core sectionupon which is mounted the primary winding 52 is provided with an air gapin order to concentrate the fiux generated by the windings 51 and 58 inthe magnetic core sections on which are mounted the windings 48 and 50.In addition the device 5| may be provided with a magnetic bypass orshunt 6| in order to limit the exciting or magnetizing current when thecore sections of the windings 7 4! and 58 are in a saturated condition.

The above described power circuit is substantially identical with thatof Fig. 3 of my above mentioned patent, in which a detailed explanationof its operation may be found. In brief, if the grids is are energizedwith components of alternating potential of peaked wave form from theirassociated rectifier excitation transformers 24, 25 and 26, the networki3, together with the associated anodes ll of the discharge device l6,will actas a half wave rectifier circuit supplying a half cycle ofalternating current to the lefthand portion of the primary winding ofthe output transformer 5. If the circuit is operating under unity powerfactor conditions, substantially 180 electrical degrees later, referredto the load circuit, the rectifier excitation will be removed from thegrids l9 and impressed upon the grids 26. The network l4 and itsassociated anodes I8 now operate as a half wave rectifier supplyingcurrent to the right hand portion of the primary winding of thetransformer I5, thus generating a half cycle of alternating current ofopposite polarity in the load circuit If the alternating current circuitI is supplying a lagging power factor load, the current willpersist inthe network l3 and its associated anodes l'l after the rectifierexcitation has been removed from the grids ii. In order to prevent thiscurrent from continuing to flow in the last anode path acting as arectifier, which would tend to cause a short'circuit in case of amoderately lowpower factor load, the grids I! receive a component ofinverter excitation of peaked wave form which, when the rectifierexcitation is removed, is eifectiveto transfer the current betweentheseveral anodes l1 and thus maintain control over the various anodepaths.

During those portions of the cycle when the network l3 and itsassociated'anodes H are operating as an inverter, the rectifierexcitation is delayed to the grids 20 associated with the anodes |8connected to the network M, to prevent the simultaneous flow of currentof more than a predetermined value in one network and its associatedanodes operating as a rectifier and in the other network and itsassociated anodes operating as an inverter, which would tend to producea short. circuit on the low frequency circuit II.

The manner in which the above described results are obtained may be bestunderstood by a detailed consideration of the operation of the gridexcitation circuit. The rectifier excitation for the groups of grids l9and 20 is supplied from the windings A of the excitation transformers24-29, inclusive, which are in turn excited by the primary windings Eenergized from the circuit Ill through a rotary phase shiftingtransformer 36. By adjusting this transformer 36 the phase of thealternating potentials impressed upon the grids may be controlled tovary the output of the networks l3 and I4 and their associated anodes ina. manner identical to that of an ordinary grid controlled rectifier.

The rectifier excitation is periodically removed from the groups ofgrids l9 and 20 by means of the windings D of the groups of rectifiertransformers 24, 25 and 26, and 21, 28 and 29, respectively. Thewindings D of each of these groups of rectifier excitation transformersare energized with unidirectional current impulses from the auxiliaryrectifier circuits 39 and 40 respectively.' These auxiliary rectifiersare energized thro 'gh a. transformer 4|4| from a source of alternatingpotential 41 of a frequency which it is desired to supply to the loadcircuit I, or, in case the load circuit II is connected to anindependent source of electromotive force for determining its frequency,it may be e directly therefrom. If it be asumed that the potentials im-5 pressed upon the grids 01 electric valves ll and I! by means of thephase-shitting circuit 53 and the self-saturating transformer ii areretarded in phase with respect to their anode potentials byapproximately 180 electrical degrew, they are maintained non-conductiveand electric valves II and II operate as simple, half wave, single phaserectifier circuits supplied with alternating potentials of oppositepolarity so that the windings D of the groups of transformers II, 25,and 28, and 21, 28, and 29 are alternately energized with positive halfcycles from the lower frequency source 41'. These windings are sodesigned as to completely saturate their associated transformers so thatwhen any of the windings D are energized no secondary voltages areproduced in the corresponding secondary coils A. In other words, whenthe windings D of either group of transformers are energized, therectifier excitation is removed from the corresponding group oi grids i9and 28.

Under the assumed conditions, it will be noted that rectifier excitationis alternately removed from the groups of grids i9 and 20 for intervalsof 180 electrical degrees referred to the load circuit. By graduallyadvancing the phase of the potential applied to the primary winding 52of the saturable transformer Si by means of the phase shiftingcircuitil, electric valves 42 and 45 may be gradually brought intooperation. If it be assumed that the phase rotation is such that thevoltages supplied to the anodes of these valves from their associatedphases of the network 4| lead the voltages applied to electric valves 43and (4, as the phase of their grid potentials is gradually advanced, theduration of the positive impulses supplied to the windings D isprogressively increased. With 120 degrees phase displacement between thewindings of network 4| connected to each of the rectifier circuits 3!and 45 40, the maximum duration for the energizatlon of the windings Dwill be 300 electrical degrees.

The phase shifting circuit 53 may thus be controlled in accordance withthe particular power factor conditions obtaining on the load circuit 50I I to supply rectifier excitation to the groups of grids l9 and 20 fora proper portion of each cycle.

It is well known that any electric valve converting apparatus or asystem including trans- 5 former windings, electric valves, etc. has acertain amount of inherent regulation; that is, a

certain drop in voltage upon increase in the load current from no loadto a full load due to the impedance of the system. In order to compen- 0sate for this natural regulation characteristic, the several rectifierexcitation. transformers are provided with the windings B, connected inseries with the load current of the network and associated anodescontrolled by the particular 65 group of transformers. The coils B arepreferably designed to only partially saturate their associated controltransformers. The eifect of this unidirectional saturation of thecontrol transformers is to advance the point in the cycle 70 ofalternating potential of the supply circuit "I at which the resultantflux in the saturable core of each of the transformers reversespolarity,

which corresponds to the instant at which a peaked impulse is suppliedto the winding A. 75 In this manner the rectifier excitaflon peaks, or

impulseatothegroupsofgridsiflandilis advanced in phase with increasingload current onthesystemtotendtoincreasetheaverage voltage impressedupon theload circuit and thus compensate for the natural regulation ofthe system.

As explained above, it is advisable continuously to provide a componentof inverter excitationtothegroupsofgrids I! andllinorder to enable thenetworks I! and I4 and theirassoelated anodes to act as inverters underreactive power factor conditions when the rectifier axcitaflon isremoved for a portion of each cycle during which current is stillflowing. This inverter excitation is provided by the windings P which,it will be noted, are connected in series with the windings A. Thesewindings are continuously excited by the windings H of the saturabletransformers 30-35, inc., the phase of the alternating potentialsimpressed upon the windings H is adjusted by means of the rotary phaseshifting transformer 31 to substantially phase opposition to thepotentials impressed upon the groups of anodes I1 and I8, making dueallowance for the necessary commutating angle.

It is well understood by those skilled in the art that when operatingconverting apparatus as an inverter it is necessary to transfer currentfrom an outgoing valve to an incoming valve at a point in the cycle ofalternating electromotive force when the counter-electromotive force ofthe incoming winding is less than. that of the outgoingwinding, so thatthere shall be a resultant electromotive force for producing thecommutation. The last moment at which this commutation would betheoretically possible would be when their counterelectromotive forcesare equal. The phase angle between the instant at which commutation isactually started and that at which itbecomes actually and theoreticallyimpossible to efi'ect commutation is referred to as the commutatingangle. This angle varies with the reactance of the circuits betweenwhich the current is to be commutated and the magnitude of the currentwhich is to be-commutated.

It is preferable that thiscommutating angle' should be kept as small aspossible in order to minimize the distortion in the wave forms of thecurrent and voltage of the system. On the other hand, it is necessarythat this commutating angle should be suilicient to provide reliablecommutation under the heaviest loads which the apparatus will encounter.

In the above described system this commutating angle may be adjusted toa minimum for light load conditions by means of the rotary phaseshifting transformer 31. The windings G of the inverter excitationtransformers 3H5 inc., are connected in series with the load current ofthe network [3 or it and its associated anodes which the particulargroup of transformers control. These windings are designed to onlypartially saturate the cores of the inverter transformers 30-35, inc.,and their effect is similar to that of the windings B of the rectifierexcitation transformers; that is, to progressively advance the phase ofthe inverter excitation in accordance with increases in load on thesystem.

In this manner the commutating angle is progressively increased so thatit may be kept at a minimum for each operating condition of the system.

When the component of inverter excitation supplied to the groups ofanodes i1 and It by the windings F of the inverter excitationtransformers 30-35, inc., leads the electromotive force of the networks13 and I4 appreciably to provide an adequate commutating angle, asdescribed above, the ratio of the voltage of the output circuit II tothat of the particular one of the networks I3 or H operating as aninverter is correspondingly lowered, as is well understood by thoseskilled in the art. If, at the same time, the rectifier excitationsupplied to the group of anodes cooperating with the network operatingas rectifier is substantially in phase with the electromotive force ofthis network, the ratio of the voltage of the alternating current loadcircuit II to the electromotive force of the networks I3 and M will be amaximum. In other words, the counter-electromotive force against whichthe rectifying apparatus is operating, is considerably less, consideringthe ratio of transformation, than the counter-electromotive forceagainst which the inverting apparatus is operating, so that acirculating current will tend to flow between the networks I3 and I4 andtheir associated anodes.

As the commutating angle is increased with increasing load on thesystem, as described above, this effect is accentuated so that anexcessive circulating current will tend to flow in the systern. Suchexcessive circulating currents are prevented by the series windings C ofthe rectifier excitation transformers. It will be noted that thesewindings C on each group of rectifier excitation transformers 24--25-26and 2l28-29 are in series with the current transmitted by the networkand its associated groups of anodes l1 or l8 controlled by the othergroup of transformers. Under very light load conditions, theunidirectional current fiowing in these windings is effective toprogressively retardthe phase of the rectifier excitation and thusdecrease the ratio of the voltage of the alternating current circuit llto that of the particular network which is operating as a rectifier tocompensate for a similar decrease in this ratio with respect to thenetwork operating as an inverter, due to the shift in phase of theinverter excitation.

To secure stable operation it is necessary that the number of turns ofthe windings C on the rectifier excitation transformers is effective toshift the phase of the rectifier excitation at a rate greater than thatat which the windings G on the inverter excitation transformer shift thephase of the inverter excitation to provide a proper commutating angle.If this were not so and the inverter excitation were shifted at a. ratehigher than the rectifier excitation; the ratio of the voltage of thecircuit H to that of .the networks I3 or'll of the apparatus operatingas an inverter would decrease faster than that operating as a rectifier,and the system would tend to build up a cumulatively increasingcirculating current and eventually go into short circuit. By properly'proportioning the ratio of the turns of the windings Cand the windingsG, however, the rectifier grid excitation may be retarded faster thanthe inverter excitation is advanced and, when the load current exceeds apredetermined value, which is preferably not more than a 'few per centof normal load current, the windings C are effective to completelysaturate their associto prevent the building up of a circulatingcurrent.

As mentioned above, in case the frequency ratio of the alternatingcurrent supply circuit l0 and v the load circuit II is non-integral, thesuccessive half cycles of alternating potential of the load circuit arenot identical but comprise groups of the supply frequency half cycleswhich may differ in number by one cycle. For example, a series of half'cycles of the low frequency potential may each comprise six half cyclesof the supply frequency which will then be followed by a half cyclecomprising seven half cycles of thesupply frequency. If these longer lowfrequency half cycles are separated by an even number of half cycles,they will always be produced by the same one of the networks I: or IIand will thus be supplied always to the same half of the primary windingof the transformer l5. The result is that the average current suppliedto the one half of the primary winding of the transformer I5 is slightlygreater than that supplied to the other half so that there is aunidirectional component of flux generated which tends to saturate thecore of the transformer l5.

In order to prevent this unidirectional saturation of the outputtransformer l5, there is provided an equalizing arrangement on theauxiliary transformer device 5| utilized for controlling the holdofl' ofthe rectifier excitation. This consists of the magnetic core section 55which is common to the saturable sections carrying the secondarywindings l9 and 50 which control the auxiliary rectifier apparatus 39and 4|! to periodically remove the rectifier. excitation from the gridsI! and 20. On this magnetic core section are mounted windings 51 and 58connected respectively in series with the current transmitted by thenet- 'works l3 and I4 and their associated anodes. The current carriedby each of these windings connetomotive force andthus substantiallyeliminate its effect upon the windings l9 and 5|.

If, however, the average current carried by one of the networks 13 or lland its associated anodes tends to become greater than the. other, whichwould resultfin a saturation of the output transformer l5, as describedabove, there is produced a resultant unidirectional magnetomotive forcein the core section 56 which is not affected by the short circuitedwinding 59 and which, due to the air gap in the core section on whichthe primary winding 52 is mounted, is forced almost completely throughthe core'sections on which. the windings l9 and 50 are wound. Due totheopposite polarity of the l8 and 50, the ef-. fect of this unidirectionalcomponent in the saturating core sections is opposite, advancing thepoint in the cycle of alternating potential at which the resultant fluxof one of the core sectionspasses through zero and retarding that of theother. The effect of..this is to advance the phase of the gridpotentialof one of the valves 42 or. 45, and retard that of the other. This results in shortening, the intervalsof rectifier exits associated anodes tocarry more than its share of the current. In this manner a very accuratebalance between the currents can'ied bythe net- 6 ao,4os

works it and Il may'be maintained to prevent saturation of the outputtransformer II.

While I have described what I at present consider the preferredembodiment of my invention, it will be obvious to those skilled in theart that various changes and modifications may be made without departingfrom my invention, and I therefore aim in the appended claims to coverall such changes and modifications as fall within the 10 true spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: 1. An electric valve converting system comprising a higherfrequency alternating current circuit, a lower frequency alternatingcurrent circuit, means including a plurality of groups of electricvalves for transmitting energy therebetween, means for exciting saidgroups of valves for inverter operation to transmit energy from saidlower frequency circuit to said higher frequency circuit, means formodifying said inverter excitation to increase the commutating anglewith increase in load current of the system, means for simultaneouslyexciting said groups of valves for rectifier operation, meansior periodically and successively removing the rectifier excitation from saidgroups of valves at the frequency of said lower frequency circuit, meansresponsive to the flow of current in each group of valves for removingthe rectifier excitation from the other valves, means responsive to theload current of the system for modifying said rectifier excitation toregulate the energy transmitted between said circuits, and meansresponsive to an unbalance in the currents transmitted by said groups ofvalves for modifying said rectifier excitation to restore a balancebetween said currents.

2. An electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating cm-rentcircuit, means including a plurality of groups of electric valves fortransmitting energy therebetween, each of said valves being providedwith a control electrode, a plurality of saturable transformers forenergizing said control electrodes with a component of said higherfrequency alter,- nating potential of peaked wave form for normallyexciting said valves for inverter operation,

means for variably and partially saturating the transformers associatedwith each group of valves in accordance with the current transmitted bythat group to vary the commutating angle of the inverting valves. aplurality of other saturable transformers for energizing said controlelectrodes with a component of said higher frequency alternatingpotential of peaked wave form for exciting said groups of valves forrectifier operation, means for periodically and successively saturatingsaid rectifier excitation transformers at the frequency of said lowerfrequency circuit, means for saturating the rectifier excitationtransformers associated with each group of valves in response to thecurrent transmitted by another group of valves, whereby only one groupof valves transmits current at any particular instant, means forpartially and variably saturat- 'ing the rectifier excitationtransformers associated with each group of valves in accordance with thecurrent transmitted by that group of valves to regulate the energytransmitted between said circuits, and means responsive to an unbalancein the current transmitted by said groups of valves for oppositelymodifying the saturation of the rectifier excitation transformersassociated therewith to restore the balance between said currents.

3. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a plurality of groups of electric valvesfor transmitting energy therebetween, each of said valves being providedwith a control electrode, excitation apparatus for said electrodescomprising means for energizing said; control electrodes with acomponent of said high-- or frequency alternating potential of peakedwave form for normally exciting said valves for inverter operation, asaturable core transformer winding included in the circuit of thecontrol electrode of each of said valves, means for inducing in saidtransformer windings a higher frequency alternating potential forexciting said valves for rectifier operation, saturating windings forsaid transformer cores, auxiliary rectifier means for energizing in apredetermined sequence the saturating windings of the transformersassociated with said groups of valves, and means for controlling saidauxiliary rectifier means to control- 'means for energizing said controlelectrodes with a component of said higher frequency alternatingpotential of peaked wave form for normally exciting said valves forinverter operation, a saturable core transformer winding included in thecircuit of the control electrode of each of said valves, means forinducing in said transformer windings a higher frequency alternatingpotential for exciting said valves for rectifier operation, saturatingwindings for said transformer cores, auxiliary polyphase rectifier meansincluding a plurality of auxiliary electric valves, circuit means forenergizing the saturating windings of the transformers associated witheach group of main valves from two phases of said auxiliary rectifierand their associated auxiliary valves, and means for controlling theconductivity of one of said auxiliary valves to control the portion ofeach cycle of said low frequency circuit during which said main valvesoperate as rectifiers.

5. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a plurality of groups of electric valvesfor transmitting energy therebetween, each of said valves being providedwith a control electrode, excitation apparatus for said electrodescomprising means for impressing upon said control electrodes analternating potential of said higher frequency and of peaked wave formto excite said valves for inverter operation, a

saturable core transformer winding including in, the circuit of thecontrol electrode of each of said valves, means for inducing in saidtransformer windings a higher frequency alternating potentialfor,exciting said valves for rectifier operation, and means responsiveto the flow of current .in one group of valves for saturating the coresof said higher frequency and of peaked wave,

form to excite said valves for inverter operation, a'saturable coretransformer winding ineluded in the circuit of the control electrode ofeach of said valves, means for inducing in said .transformer windings ahigher frequency alternating potential for exciting said valves forrectifier operation, and a saturating winding for each of saidtransformer cores, the saturating windings of the transformer coresassociated with one group of valves being connected to carrya currentproportional to the current transmitted by the other group of valves anddesigned completely to saturate their respective transformer coreswhereby the simultaneous operation of said groups of valves isprevented.

'7. In an electric valve converting system comprising a supply circuit,a load circuit, one of 3 said circuits being an alternating currentcircuit, and means including a plurality of electric valves 'fortransmitting energy therebetween, each of 'said valves being providedwith a control electrode, excitation apparatus for said electrodescomprising a control circuit for eachof said valves including asaturable core transformer winding, means for exciting said transformerwindings with an alternating potential of the frequency of saidalternating current cir- 40 cult, and means for variably saturating thecores of 'said transformer windings in response to the load current ofthe system to regulate the energy transmitted from said supply circuitto said load circuit.

8. In an electric valve frequency converting system comprising analternating current supply circuit, an alternating current load circuitand means including a plurality of electric valves for transmittingenergy therebetween, each of said valves being provided with a controlelectrode, excitation apparatus for said electrodes comprising asaturable core transformer wind ing included in the circuit of thecontrol electrode of each of said valves, means for energizing saidtransformer windings in a predetermined sequence with alternatingpotentials of the frequency of said supply circuit and of a phase toexcite said valves for rectifier operation, and means for variablysaturating the cores of said transformer windings in response to theload current of the system to regulate the energy transmitted from saidsupply circuit to said load circuit.

9. In an electric valve converting system comprising a higher frequencyalternating current supply circuit, a lower frequency alternatingcurrent load circuit, and means including a plurality of groups ofelectric valves for transmitting energy therebetween, each of saidvalves being provided with a control electrode, excitation apparatus forsaid electrodes comprising means for impressing upon said controlelectrodes an alternating potential of said higher frequency and ofpeaked wave form to excite said valves for 7 inverter operation, asaturable core transformer some winding included in the circuit of thecontrol electrode of each of said valves, means for Minducing in saidtransformer windings a higher frequency alternating potential forexciting said valves for rectifier operation, and means responsive tothe flow of current in each group of electric valves for varying thesaturation of its associated control transformers to regulate theenating potential of said higher frequency and of peaked-wave form toexcite said valves for inverter operation, a saturable core transformerwinding included in the circuit of the control electrode ofeach of saidvalves, means for inducing in said transformer windings a higherfrequency alternating potential for exciting said valves for rectifieroperation, and a saturating winding for each of said transformer cores,the saturating windings of the transformer cores associated with eachgroup of valves being connected to carry a current proportional to thecurrent transmitted by their respective group of valves and designed tovariably and incompletely saturate their respective transformer cores toregulate the energy transmitted from said supply circuit to said loadcircuit.

11. In an electric valve converting system comprising a supply circuit,a load circuit, one of said circuits being an alternating currentcircuit, and means including a plurality of electric valves fortransmitting energy therebetween, each of said .valves being providedwith a control electrode,

excitation apparatus for said electrodes comprising a control circuitfor each of said valves including a saturable core transformer winding,means for energizing said transformer windings in a predeterminedsequence with alternating potentials of the frequency of saidalternating current circuit and of a phase to excite said valves forinverter operation, and means for variably saturating the cores of saidtransformer windings in response to the load current of the system toincrease the commutating angle with increasing load.

12. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a plurality of groups of electric valvesfor transmitting energy therebetween, excitation apparatus for saidsystem comprising means for exciting one of said groups of valves forrectifier operation to transmit energy from the higher frequency circuitto the lower frequency circuit, means for simultaneously excitinganother group of valves for inverter operation to transmit energy fromthe lower frequency circuit to the higher frequency circuit, and meansresponsive to the load current of the system for modifying said inverterexcitation to control the commutating angle.

13. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a plurality of groups of electric valvesfor transmitting energy therebetween, each of said valves being providedwith a control electrode, excitation apparatus for said systemcomprising means for exciting one of said groups of valves for rectifieroperation to transmit energy from the higher frequency circuit to thelower frequency circuit, means for simultaneously energizing the controlelectrodes of another group of valves with an alternating potential ofsaid higher frequency to excite said valves for 10 inverter operation,and means for varying the phase of said inverter excitation inaccordance with the load current of the system to vary the commutatingangle.

14. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a plurality of groups of electric valvesfor transmitting energy therebetween, each of said valves being providedwith a control electrode, excitation apparatus for said electrodescomprising means for impressing upon said control electrodes analternating potential of said higher frequency and of peaked wave formto excite said valves for rectifier operation, a saturable coretransformer winding included in the circuit of the control electrode ofeach of said valves, means for inducing in said transformer windings ahigher frequency alternating potential for exciting said valves forinverter operation, and means responsive to the flow of current in eachgroup of valves for varying the saturation of the cores of thetransformer windings associated therewith to vary the commutating angle.

15. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a plurality of groups of electric valvesfor transmitting energy therebetween, each of said valves being providedwith a control electrode, excitation apparatus for said electrodescomprising means for impressing upon said control electrodes analternating potential of said higher frequency and of peaked wave formto excite said valves .for rectifier operation, a' 5 saturable coretransformer winding included in the circuit of the control electrode ofeach of said valves, means for inducing in said transformer windings ahigher frequency alternating poten-' former cores to regulate thecommutating angle at which the inverting valves of the system operate.

16. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a plurality of groups of electric valvesfor transmitting energy there- 35 between, excitation apparatus for saidsystem comprising means for successively exciting said groups of valvesfor rectifier operation to transmit energy to said low frequencycircuit, and means for modifying said rectifier excitation in responseto an unbalance in the currents transmitted by said groups of valves.

17. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a plurality of groups of electric valvesfor transmitting energy there- I.

prising a higher frequency alternating current circuit, a lowerfrequency alternating current circuit, and means including a pluralityof groups of electric valves for transmitting energy therebetween,excitation apparatus for said system comprising means for exciting saidgroups of valves for 'rebttfier operation to transmit energy from saidhigh frequency circuit to said low frequency circuit, means includingauxiliary electric valve means for successively removing said rectifierexcitation from said groups of valves at the frequency of said lowfrequency circuit, a transformer device provided with an excitingwinding connected to be energized at said low frequency and with asaturable magnetic core section and a secondary winding mounted thereonand connected to control said auxiliary valve means, and means forsaturating said magnetic core section in accordance with an unbalance inthe currents transmitted by said groups of valves.

19. In an electric valve converting system comprising a higher frequencyalternating current circuit, a lower frequency alternating currentcircuit, and means including a pair of groups of electric valves fortransmitting energy therebetween, excitation apparatus for said systemcomprising means for exciting said groups of valves for rectifieroperation to transmit energy from said high frequency circuit to saidlow fre-- quency circuit, means including a pair of auxiliary electricvalve means each connected to periodically remove said rectifierexcitation from one of said groups of valves at the frequency of saidlow frequency circuit, a transformer device providedwith an excitingwinding connected to be energized at said low frequency and with a pairof saturable, magnetic core sections, each having a winding connected tocontrol one of said auxiliary valves means, the saturable magnetic coresections having a common magnetic path, and a winding connected inseries with each of said groups of valves, said windings beingdifferentially mounted to link the common magnetic path of said coresections and the windings mounted onsaid saturable core sections beingconnected to be oppositely influenced by a differential magnetization oftheir common path.

20. In an electric valve translating circuit, a source of alternatingpotential, 2. self-saturating transformer energized therefrom andprovided with a secondary winding in which is'induced an alternatingpotential of peaked wave form, an auxiliary saturating winding for saidtransformer, a source of periodic current connected to said winding,said periodic current having a unidirectional component effective todetermine the phase of the secondary alternating potential of peakedwave form, and means for substantially eliminating the eifect of theperiodic component of said periodic current upon the phase of saidsecondary potential.

21; In an electric valve translating'circuit, a source of alternatingpotential, a self-saturating transformer energized therefrom andprovided with a secondary winding in whichis induced an alternatingpotential of peaked wave form, a 'source of periodic current having aunidirectional component, a saturating winding for said transformerenergized from said source of periodic current, and an additionalwinding for said v n transformer closed through a low impedance path andeifectiv'e to reduce to substantially zero the flux of said transformerdue to the periodic component of said periodic current.

22. In an electric valve translating circuit, ,a 15 source ofalternating potential, a self-saturating transformer energized therefromand provided with a secondary winding in which is induced an alternatingpotential of peaked wave form, a pair of auxiliary saturating windingsfor. said transformer, and two sources of periodic current eachconnected to one of said saturating windings, each of said periodiccurrents having a unidirectional component and the algebraic sum of saidunidirectional components being effective to determine the phase of thesecondary alternating potential of peaked wave form. 23. In an electricvalve translating circuit, a

or ..i

source of alternating potential, a self-saturating 35 sources, theresultant of the unidirectional com- I ponents of said periodic currentsbeing effective to determine the phase of the secondary alternatingpotential of peaked wave form, and means for substantially eliminatingthe effect of the periodic component of said. periodic currents upon thephase of said secondary potential.

24. In an electric-valve converting system comprising a higherfrequencyalternating current circuit, -a lower frequency alternatingcurrent circuit, means including a plurality of electric valves fortransmitting energy therebetween, excitation apparatus for said systemcomprising means for exciting one group of valves for rectifieroperation to transmit energy from the higher 50 frequency circuit to thelower frequency circuit a and means for exciting another group of valvesfor inverter operation, means responsive to the current transmitted bysaid valves for shifting the phase of said inverter excitation, andcurrent 55 responsive means for shifting the phase of the rectifierexcitation at the proper rate and sense to prevent a circulating currentfrom flowing between said groups of valves.

25. In an electric valve converting system come '60 prising a higherfrequency alternating current circuit, a lower frequency alternatingcurrent circuit, means including a plurality of groups of electricvalves for transmitting energy therebetween, excitation apparatus forsaid system com- 65 prising means for exciting one of said groups ofvalves for rectifier operation to transmit energy from the higherfrequency circuit to the lower frequency circuit and means forsimultaneously exciting another group of valves for inverter op- 70eration to transmit energy in the opposite direction, means for shiftingthe phase of the inverter excitation in response to current transmittedby said valves, and means for shifting the phase of the rectifierexcitation at a rate greater thanthe 75 rate of phase shift of saidinverter excitation.

26. In an electric valve converting system com-. prising a higherfrequency alternating current circuit, a lower frequency alternatingcurrent circuit, means including a plurality of groups of electricvalves for transmitting energy therebetween, excitation apparatus forsaid system comprising means for exciting one of said groups of valvesfor rectifier operation, means for exciting simultaneously another groupof valves for inverter operation, means for shifting the phase of saidinverter excitation in response to current transmitted by said system,and means for shift ing in opposite sense the phase of said rectifierexcitation at a rate greater than the rate of phase shift of saidinverter excitation, said latter means operating to remove saidrectifier excitation in response to current-in excess of a predeterminedamount. I

27. In an electric valve converting system comprising a supply circuit,a load circuit, one of said circuits being an alternating currentcircuit,

means including a plurality of electric valves for transmitting energytherebetween, each of said valves being provided with a controlelectrode, excitation apparatus for said electrodes of said valvescomprising means for exciting some of said valves for rectifieroperation, means for exciting others of said valves for inverteroperation, means for shifting the phase of the inverter excitation inresponse to current transmitted by said valves, and means for shiftingthe phase of the rectifier excitation at a rate greater than the phaseshift of said inverter excitation.

28. In an electric valve converting system comprising a higher frequencyalternating current line, a lower frequency alternating current line,

electron discharge means comprising a plurality of electrically distinctcircuits, means for connecting said discharge means with each of saidcircuits, means for controlling the operation of said discharge means,and means responsive to the-flow of current through one of said circuitsmit energy to said low frequency circuit, and an electrical interlockfor preventing simultaneous operation of said groups. of valves.

30. In an electric current converting system, an alternating currentline, a second electric current line, electron discharge meanscomprising a plurality of electrically distinctcircuits, means forconnecting said discharge means with each of said lines, means forcontrolling. the operation of said discharge means, and means responsiveto the flow of current through one of said circuits to prevent flow ofcurrent through another of said circuits.

31. In an electric current converting system, an electric current line.a second electric current line, a plurality of electrically distinctelectron. discharge devices each having anodes with associated controlelectrodes and a cathode, means for connecting said discharge deviceswith each of said lines, means for energizing the control electrodes ofsaid devices, and means resp'onsirfi: to the flow of current through oneof said disprising a supply circuit, a load circuit, one of said pliedby said rectiflers, a current transformer in 5 circuits being analternating current circuit, the output circuit of each rectifier, saidcurrent mean including a plurality of groups of electric transformeractuating a grid for preventing curvalves for transmitting energytherebetween, rent flow in the other rectifier while current flows eachof said valves being provided with a control in the current transformer.

electrode, excitation apparatus for said elec- 36. In a reversibleelectric current converting 1o trodes of said valves comprising meansfor excitsystem; an elecltrig. curseigghliiie, a second elecfirzc ingsome of said valves for rectifier operation, curren line, eec ron argemeans comp means for exciting others of said valves for ining aplurality of electrically distinct circuits, verter operation, and aninterlock comprising means for connecting said dilcharge means with acurrent transformer associated with each group each of said lines, meansfor controlling the op- 15 of valves and grids controlled by saidcurrent eration of said discharge means, and means retransformer forpreventing simultaneous current spons ve t e fl w fl 8 One flow in saidgroups of valves. said circuits to prevent flow of current through 33. Afrequency converter comprising a pluanother 0! said mrality ofmercury-arc rectiflers, an alternating In a reversible elecmlfhcumntmnvlertmg 20 current source for supplying said rectiflers, an I i agz galternating current circuit fed alternately by said S22E2 g g g achhavmyg modes rectiflers, and an electrical interlock for preventwithassociated control 81 trodes and a cathode 25 ing simultaneous operationof said rectiflers. means for connecting said discharge devices with as4. A frequency converter comprising a plueach of said lines, meansenergizing fh! com rality oi mercury-arc rectiflers, an alternating no!electrodes of said devices and means w current source for supplying saidrectiflers, an Sponsive to the fl of current through one of alternatingcurrent circuit fed alternately by said Said discharge devices operableto prevent the so rectifiers, an interlock comprising a current flow ofcurrent through another of said discharge so.

charge devices operable to prevent the flow of current throughanother'of said discharge devices.

32.' In an electric valve converting system comtransformer associatedwith each rectifier and grids controlled by said current transformersfor Reissue No. 20,i .93.v

preventing simultaneous current flow in said transformers.

35. A frequency converter comprising a plurality of rectiflers, anoutput transformer supdevices.

BURNICE D. BEDFORD.

CERTIFICATE OF CORRECTION.

BURNICE D. BEDFORD.

It is hereby certified that error appears in the printed specificationof the above numbered'patent requiring correction as follows: Page 1,first column, line 1 .8, for the word "frictional" read fractional; page8, second column, linejfi, claim 19, for "valves" read valve; and thatthe said Letters Patent shouldbe read with these corrections thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 19th day of October, A. D. 1957.

Henry Van Aradale.

(Seal) Acting Commissioner of Patentsr charge devices operable toprevent the flow of current through another'of said discharge devices.

32.' In an electric valve converting system comprising a supply circuit,a load circuit, one of said circuits being an alternating currentcircuit, mean including a plurality of groups of electric valves fortransmitting energy therebetween, each of said valves being providedwith a control electrode, excitation apparatus for said electrodes ofsaid valves comprising means for exciting some of said valves forrectifier operation, means for exciting others of said valves forinverter operation, and an interlock comprising a current transformerassociated with each group of valves and grids controlled by saidcurrent transformer for preventing simultaneous current flow in saidgroups of valves.

33. A frequency converter comprising a plurality of mercury-arcrectifiers, an alternating current source for supplying said rectiflers,an alternating current circuit fed alternately by said rectiflers, andan electrical interlock for preventing simultaneous operation of saidrectiflers.

34. A frequency converter comprising a plurality of mercury-arcrectiflers, an alternating current source for supplying said rectiflers,an alternating current circuit fed alternately by said rectifiers, aninterlock comprising a current transformer associated with eachrectifier and grids controlled by said current transformers for ReissueNo. 20,i .93.v

BURNICE D. BEDFORD.

preventing simultaneous current flow in said transformers.

35. A frequency converter comprising a plurality of rectiflers, anoutput transformer supplied by said rectiiiers, a current transformer inthe output circuit of each rectifier, said current transformer actuatinga grid for preventing current flow in the other rectifier while currentflows in the current transformer.

36. In a reversible electric current converting system, an electriccurrent lirie, a second electric current line, electron discharge meanscomprising a plurality of electrically distinct circuits, means forconnecting said discharge means with each of said lines, means forcontrolling the operation of said discharge means, and means responsiveto the flow of current through one of said circuits to prevent flow ofcurrent through another of said circuits.

37. In a reversible'electric current converting system, an electriccurrent like, a second electric current line, a plurality ofelectricallydistinct electron discharge devices each having modes with associatedcontrol electrodes and a cathode, means for connecting said dischargedevices with each of said lines, means for energizing the controlelectrodes of said devices, and means responsive to the flow of currentthrough one of said discharge devices operable to prevent the flow ofcurrent through another of said discharge devices.

BURNICE D. BEDFORD.

CERTIFICATE OF CORRECTION.

September '1, 1957 It is hereby certified that error appears in theprinted specification of the above numbered'patent requiring correctionas follows: Page 1, first column, line 1 .8, for the word "frictional"read fractional; page 8, second column, linejfi, claim 19, for "valves"read valve; and that the said Letters Patent shouldbe read with thesecorrections therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 19th day of October, A. D. 1957.

(Seal) Henry Van Arsdale. Acting Commissioner of Patentsr

